What is the symbolism of the apartment key in Zikora: A Short Story?

Zikora's apartment key symbolizes finality. Not long after Kwame leaves her, he mails her apartment key back to her in an envelope. Though Zikora insists that she cannot understand why he has done this, desperate for him to return and explain himself, his gesture represents the end of their relationship. Zikora's refusal to acknowledge the meaning of the key's return, proves her reluctance to letting Kwame go.